818 
FXUS63 KLMK 301116
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
616 AM EST Mon Nov 30 2020

.Forecast Update...
Issued at 610 AM EST Mon Nov 30 2020

Upper wave has kicked well into eastern Kentucky, with cooler air 
aloft spilling into the lower Ohio Valley behind it. We have seen an 
initial corridor of colder air at the surface from south-central 
Kentucky up into the Bluegrass region, and that has cooled just 
enough to allow for intense enough snowfall to accumulate on grassy 
and elevated surfaces. Other than that, the forecast remains well on 
track, and the Winter Weather Advisory for late afternoon into 
tonight will not be modified. 

The ongoing snow will be covered in a Special Weather Statement, as 
any impacts are expected to be brief and limited. Pavement temps are 
still in the 40s, so even where there is some slushy snow (such as 
bridges/overpasses) it will melt fairly quickly once the snowfall 
lightens up.

&&

.Short Term...(Today and tonight)
Issued at 330 AM EST Mon Nov 30 2020

...FIRST ACCUMULATING SNOW EXPECTED TONIGHT...

Upper wave lifting through the Tennessee Valley, with mid-level 
frontogenesis focusing a band of moderate precip mainly affecting 
Middle Tennessee and central Kentucky. It's almost entirely rain so 
far, but we are seeing a slot of colder temps, generally 33-35F, 
punching up the I-65 corridor into south central Kentucky. 

In the very near term, we'll be watching the intensity of the precip 
shield lifting out of Middle Tennessee as it meets the incoming 
colder air, as that could focus a band of slushy snow accumulations 
during the morning commute. Right now the best chance for that 
appears to be setting up from the Lake Cumberland area to just south 
of Lexington and Frankfort. However, with the precip in TN showing a 
weakening trend, confidence is limited enough that we will only be 
able to do short-fuse messaging as we actually see a band of 
accumulating snow develop. 

Look for a rain/snow mix for a lot of the day under the upper cold 
pool with plenty of wraparound moisture, and some localized Lake 
Michigan enhancement. Temperatures remain quite flat in the 
mid/upper 30s, just warm enough to prevent any daytime accumulation 
even with intermittent changes to all snow. Precip will taper from 
west to east late in the afternoon as wraparound moisture departs. 

Temps will drop below freezing just after sunset, with snow showers 
continuing east of a line from roughly Madison, IN to Lake 
Cumberland. This area could pick up around 1 inch of accumulation as 
surface temps continue to drop, resulting in impacts to travel. 
Current advisory matches up pretty well with the 50-60% probability 
of 1 inch accumulation and we can't rule out localized 2 inch 
amounts across the Bluegrass region in KY, where we could see better 
enhancement from the Lake Michigan plume. Winter Weather Advisory 
will remain as-is.  

It's worth noting that the Advisory runs through 7 AM Tuesday, but 
with temps expected to be in the mid 20s at that time, travel 
impacts could linger through the Tuesday morning commute even after 
the snow ends.

.Long Term...(Tuesday through Sunday)
Issued at 300 AM EST Mon Nov 30 2020

Tuesday looks cold and breezy to begin the long term, with low 
clouds lingering east of I-65 at sunrise. Portions of the Bluegrass 
region could see flurries linger into Tue morning. Though moisture 
depth will be much shallower, the saturated layer does reach up to -
10 C during the morning hours. Areas west of I-65 should wake up to 
more sunshine. The clearing line will gradually push east through 
the day. Thanks to cold air and breezy winds, wind chills will begin 
the day in the teens and will only make it into the 20s and low 30s 
during the afternoon. 

Shortwave ridging and sfc high pressure will exert their influence 
on our weather through Wednesday. Tue night will be cold and clear 
with lows in the low to mid 20s. Upper teens in typically cooler 
locations, such as valleys, seems like a decent bet. Fair weather 
continues Wednesday with highs in the 40s. 

There remains good agreement on a closed upper system and weak sfc 
reflection rotating across KY and southern IN Wednesday night 
through Thursday night, bringing light precipitation to the region. 
Timing and QPF discrepancies linger, however, with GFS/CMC solutions 
notably faster than the ECMWF. There does appear to be some diurnal 
variability in p-type, with plain rain likely winning out during the 
daytime on Thursday. But decided to lean on the relatively low 
PoPs/QPF from NBM for now. Lows are likely to be below freezing Thu 
morning with highs in the 40s. Fri morning should be a touch warmer 
with lows in the low to mid 30s. 

Model consistency suffers by the weekend, though it does appear a 
notable trough may dive southeast over the Upper Ohio Valley late in 
the weekend. Without a meaningful signal, going to stick with a dry 
forecast through the weekend. Chilly temperatures are likely to 
continue during this time.

&&

.Aviation...(12Z TAF Issuance)
Issued at 610 AM EST Mon Nov 30 2020

Tongue of colder air has pushed into LEX and helped transition 
precip to a decent snow, resulting in LIFR conditions and could 
accumulate on elevated surfaces in the next couple of hours. SDF, 
BWG, and HNB are all MVFR and still showing NW winds less than 10 
kt. 

Leading edge of some stronger NW winds and cold advection just 
getting into HNB and will continue to press eastward through the 
morning. This will also help the switch to all snow, and could bring 
brief IFR ceiling and vis.  Wind speeds around 15 kt with gusts near 
25 kt could result in crosswind issues, especially at LEX but 
possibly SDF as well.  

Precip tapers off around sunset or just after at SDF, HNB, and BWG, 
with ceilings lifting to VFR. LEX will struggle through the evening 
with IFR cig/vis in continued snow showers, and temps dropping below 
freezing. Crosswinds will continue with gusts near 20 kt. Cig/vis 
will finally lift after midnight in LEX.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory from 4 PM this afternoon to 7 AM EST 
     Tuesday for INZ079.

KY...Winter Weather Advisory from 4 PM EST /3 PM CST/ this afternoon 
     to 7 AM EST /6 AM CST/ Tuesday for KYZ032>037-039>043-
     047>049-055>057-066-067-078-082.

&&

$$

Update...RAS
Short Term...RAS
Long Term...EBW
Aviation...RAS